Tehee

3/Assignment.hs

@@ -0,0 +1,25 @@
+{-# Language LambdaCase #-}
+module Assignment where
+
+import Chi
+
+subst :: Variable -> Exp -> Exp -> Exp
+subst var e = \case
+  Apply e1 e2 -> Apply (subst var e e1) (subst var e e2)
+  Lambda x e' -> Lambda x $ if var /= x then (subst var e e') else e'
+  Var x -> if var == x then e else Var x
+  Const c es -> Const c $ map (subst var e) es
+  Rec x e' -> Rec x $ if var /= x then (subst var e e') else e' 
+  Case e' branches -> Case (subst var e e') $ map substBr branches
+    where
+      substBr :: Br -> Br
+      substBr (Branch c vs e') = Branch c vs $ if var `notElem` vs then (subst var e e') else e'
+
+eval' :: Exp -> Reader (Map Variable Exp) Exp
+eval' = undefined
+
+eval :: Exp -> Exp
+eval = undefined
+
+main :: IO ()
+main = getLine >>= print . eval . parse